This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. Section 119 from an application for APPARATUS AND METHOD FOR FABRICATING HOLEY OPTICAL FIBER, filed with the Korean Industrial Property Office on Apr. 18, 2000 and there duly assigned Serial No. 20285-2000.
1. Field of the Invention
The present invention relates generally to an optical fiber, and more particularly to an apparatus and method for fabricating an optical fiber having a plurality of air holes.
2. Description of the Related Art
A holey optical fiber consists of a plurality of submicron-sized air holes running the length of a silica fiber in the cladding layer to confine light (by modified total internal reflection) to a core layer. The holey optical fiber finds its increased applications as a waveguide with novel properties for dispersion compensated fiber communications, non-linear fiber and grating applications, and optical fiber amplifications.
Basically, the holey optical fiber includes a dielectric structure with a refractive index that varies periodically across a transverse plane but is uniform in the normal direction. This dielectric structure causes Bragg diffraction and allows the holey optical fiber to have a xe2x80x9cphotonic band gapxe2x80x9d at a specific wavelength or with respect to a light wave propagation direction. The xe2x80x9cphotonic band gapxe2x80x9d refers to a condition in which light of certain frequencies will not propagate in the material and is analogous to the familiar electronic band gap, except that it applies to photons instead of electrons.
Accordingly, light can behave in unfamiliar ways, traveling along the holey optical fiber due to the photonic band gap effect and the reflective index characteristics. For details, see T. A. Birks, et. al., Electronic Letters, vol. 31(22), p. 1941, October, 1995 and J. C. Knight, et. al., Proceeding of OFC, PD 3-1, February, 1996.
In the conventional method of fabricating the holey optical fiber, an optical fiber preform is typically formed by arranging a plurality of hollow cylindrical glass tubes with a predetermined form along the cladding layer. At the same time, a core preform rod is inserted to be used depending on the application purposes, i.e., as an optical fiber amplifier, an optical fiber grating, or a non-linear optical fiber. Thereafter, the ends of the glass tubes are sealed, then the optical fiber is drawn from the preform. Accordingly, the resulting optical fiber has a plurality of submicron-sized air holes in the cladding.
In the conventional holey optical fiber, however, the outer air holes are typically closed or are much smaller than the inner air holes of the fiber. Hence, during the drawing of an optical fiber from the preform, relatively large inner air holes are transformed to an oval shape since the outer glass tubes are melted faster than the inner glass tubes due to the difference in the heat conductivity between the inner portion and the outer portion of the optical fiber preform. This type of distortion in the air holes makes the continuous mass production of holey optical fibers very difficult.
It is, therefore, an object of the present invention to provide an apparatus and method for fabricating a holey optical fiber by vertically arranging a plurality of glass tubes in a gel to prevent the distortion of air holes during the drawing step of the optical fiber.
According to another aspect of the invention, the method for fabricating the holey optical fiber is executed as follows. A sol is first formed by mixing a starting material, deionized water, and an additive. The sol is filled into a circular frame and gelled, and a preform rod is inserted into the center of the resulting gel. Meanwhile, a plurality of glass tubes is vertically arranged around the preform rod in the gel. Then, the gel is removed from the circular frame and dried. The dry gel is glassified through a heat application during the sintering process. Thereafter, the holey optical fiber is drawn from the holey optical fiber preform resulting from the sintering process by supplying gas into the ends of the air holes in the holey optical fiber preform while heating the other ends of the air holes.
According to further aspect of the invention, the apparatus for fabricating the holey optical fiber, as described in the preceding paragraphs, is installed by the following means. One end of the holey optical fiber preform is sealed with a preform cover. A gas supplier supplies gas into the preform cover. A pressure regulator regulates the amount of gas supplied from the gas supplier to be constant. A heater is installed at the other end of the holey optical fiber preform for heating the other end of the preform to draw an optical fiber.